Sitting balance II: reach direction and thigh support affect the contribution of the lower limbs when reaching beyond arm's length in sitting.

The effects of reach direction and extent of thigh support on the contribution of the lower limbs during seated reaching were examined. Twelve healthy subjects aged 59-79 years performed self-paced reaching forwards and diagonally to both sides and under three thigh support conditions. Vertical ground reaction forces (GRF) and leg muscle activity were monitored bilaterally. Reach direction affected both the magnitude of peak vertical GRF and the relative distribution of vertical GRF through the feet, demonstrating that the lower limbs work cooperatively to control the motion of the body mass. Extent of thigh support also affected the magnitude of peak vertical GRF through the feet. In addition, the EMG data confirmed the active contribution of the lower limbs when reaching beyond arm's length, with muscles in both lower limbs activated in all trials.